Rapid scanning stopped-flow enzyme concentration

Seven-coordinate three-dimensional metal complexes are considered to be quite unstable and kinetically labile species, and their solution chemistry is largely undefined. Over the last few years it was shown that these species exhibit extremely interesting chemical properties and catalytic activity. They can catalyze disproportionation of deleterious superoxide radicals, even faster than natural enzymes, and therefore this became a challenging research area. Recently, Rudi van Eldik reported a detailed rapid-scan stopped-flow kinetic study of the substitution behavior of the seven-coordinate [Fe(dapsox)(L)2]C104 complex with thiocyanate as a function of the thiocyanate concentration, temperature, and pressure in protic and aprotic organic solvents. 

Fig. 20. Rapid-scanning, stopped-flow spectra (A), difference spectra (B), and singlewavelength, stopped-flow time courses at 300, 422, and 485 nm (C, D, E) for the y-elimination reaction of CGS with OSH S. Data were obtained as described in Figure 19. All concentrations refer to conditions immediately after mixing [OSHS] = lOmM, [CGS] = 6.25 pM, 0.1 M potassium phosphate, 1 mM EDTA, pH 7.2 at 25°C. (A) RSSF spectra, Trace 0 is the spectrum of the enzyme in the absence of substrates. The initiation of scanning occurred 1.3 ms after flow stopped. Spectra shown were collected at 1.3,10.2, 19.1, 28.0, 36.9, 72.5, 117.0, 161.5, 250.5, 392.9, and 695.5 ms after flow stopped. (B) Difference spectra were computed as (scan)t-(scan)0 from the data presented in (A). Singlewavelength time courses (C-E) were collected in SWSF experiments under conditions identical with those described for (A). [Taken from Brzovic et al. (107) with permission.]...

Fig. 16. Rapid-scanning data for the reactions of 5 mM indole (A) and 5 mM benzimidazole (B) with 17.2 iM tryptophan indole-lyase (tryptophanase) that has been preequilibrated with 0.25mM t-alanine. i-Alanine was premixed in both syringes to prevent unwanted concentration changes. In panel A, scans were collected at 15,92.5,170,247.5, 325,402.5,480,557.5, 635, 712.5, 790,867.5, and 945 ms after flow stopped. Spectrum 0 represents the spectrum of the enzyme-alanine complex before mixing with indole. In panel B, scans were collected at 15, 390, 765, 1140, 1515, 1890, 2265,2640, 3015,3390, 3765, and 4140 ms after mixing. Spectrum 0 represents the enzyme-alanine complex before mixing with benzimidazole. [Taken from Phillips (104) with permission.]...

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